§ Chapter 16 IRC 2021
Duct Systems
8 entries from Chapter 16 of IRC 2021, organized by section number. Each entry covers what the code requires, why it exists, what inspectors look for, and common mistakes.
§ 01 Sections
All 8 entries.
Sorted by section number. Click any row for the full entry — answer, requirements, edition diff, related sections.
Section
Title
Question
M1601.1
Supply Ducts Must Use Approved Materials and Construction
M1601.1
What materials are allowed for HVAC supply ducts in a house?
What materials are allowed for HVAC supply ducts in a house?
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M1601.1.1
Building Cavities Are Not Ordinary Supply Ducts
M1601.1.1
Can wall cavities be used as supply air ducts?
Can wall cavities be used as supply air ducts?
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M1601.1.2
Underground Ducts Need Materials Listed for Buried Use
M1601.1.2
Can HVAC ducts be buried under a slab?
Can HVAC ducts be buried under a slab?
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M1601.4.1
Duct Joints and Seams Must Be Sealed
M1601.4.1
Do HVAC duct joints have to be sealed with mastic or tape?
Do HVAC duct joints have to be sealed with mastic or tape?
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M1601.4.2
Ducts Outside Conditioned Space Need Required Insulation
M1601.4.2
Do ducts in an attic or crawl space need insulation?
Do ducts in an attic or crawl space need insulation?
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M1601.4.3
Flexible and Metal Ducts Need Proper Support
M1601.4.3
How often do flexible ducts need to be supported?
How often do flexible ducts need to be supported?
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M1602.2
Return Air Cannot Be Taken From Prohibited Locations
M1602.2
Can a return air grille be in a garage, closet, attic, or crawl space?
Can a return air grille be in a garage, closet, attic, or crawl space?
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M1602.3
Return Air Openings Must Be Sized and Located Correctly
M1602.3
Can a furnace closet use the door louver as return air?
Can a furnace closet use the door louver as return air?
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§ 02 Chapter navigation